NEED ADVICE: how to get my man to WANT to spend more time with me

so i met Bob* a lil over a year ago, and well we got pregnant after a few dates. anyway we split about 2 months later. and didn't talk TOO much through my pregnancy. I have two other kids from a previous relationship as well. anyway we "hooked" back up from about jan to the beginning of march. we were only like "hanging out"

he didn't want a relationship right then. I knew he was talking to other girls online, like he was trying to find someone else to date.
so one day i decided that i was done messing with him. I just sent him a email saying i didn't have anything else to say to him anymore.

well a few days went by maybe a week, and i got a email from him saying just I MISS YOU!!!!
my heart stopped in my stomach. I loved this man. so i gave in and i met him that fri for dinner. He never acted the way he did that nite anytime before when we were "hanging" out i could just tell he cared and wanted to b w/me.

it's been a lil over a month and things r great. we love each other, but i feel like i NEVER EVER see him and anytime i mention it to him he acts like i ALWAYS have a problem. He works like 5-6 days a weeks and live like 30-45 min away. as i mentioned i have two other kids besides ours, so i can't just bring them to his house during the week. but it's like it doesn't bother him if he doesn't see me or help out with our son. I go to school full time, work and take care of all of them daily. He may come over once maybe twice a week and may stay one nite out. But he gets off at like 4 and doesn't come over till like 6 or 7?! by then our son's about to go to bed and hell we have to go to bed shortly(if he stays). He may stay here the weekends i have my kids, but he'll come over really late on fri or Sat and then leave early the next morn. and NEVER offers to help with OUR son. the weekends my ex has the other 2 i go to his house.
how can i get him to WANT to come over here w/o nagging and bitching about it to where I FEEL he feels like he HAS to.? and how can i get him to want to b here more or spend more time with us. I know he cares, that's not the issue, he is just a really selfish person and i can't and don't want to change that. What do i do? i feel neglected...am i overreacting?

any advice will help even if it's something i am doing wrong

I don't know what to say. It sounds like you are in a very messy situation. You have three kids one which is his. You are doing a lot of the work all by yourself, frankly I don't understand how you manage to balance, work, study and looking after three kids all by yourself. But, the way I see it your kids are your top priority. It doen't sound like this guy treats your relationship with as much commitment and seriousness as he should. You need to find a way to bring this up to him somehow, that at the very least he has responsibility as a parent that he is neglecting.

Oh, my freakin' God.

Just.... oh, my God.

i would suggest condoms.

How do I say this... um... kids are a BIG deal!!!

What exactly makes a man who doesn't find it necessary to participate in a life with his child loveable?